J. CHEM. SOC. DALTON TRANS.
1990
1119
Synthesis and X-Ray Crystal Structure of the Bis( imino) Cyclodiphosphazane,
[ ( PhN) P( NMe,) ( NPh)],t4
Santhanathan S. Kumaravel and Setharampattu S. Krishnamurthy *
Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore-560 0 12, India
T. Stanley Cameron and Anthony Linden
Department of Chemistry, Dalbousie University, Halifax, Canada B3H 4J3
The reaction of trans- [ (PhN) P( NMe,)], (1) with 2 equivalents of phenyl a i d e yields the bis( imino)
derivative, trans-[(PhN)P(NMe,)(NPh)], (2).TheX-ray crystal structure of (2)reveals that the
N,P, ring and the phenyl groups attached to the ring nitrogen atoms are coplanar. The ring
nitrogen atoms as well as the nitrogen atoms of the dimethylamino groups display trigonal planar
geometry. The bond length of 1.518 A for the exocyclic P=N bond indicates that this bond is not
delocalised with the N,P, ring system.
Structural features of four-membered N2P2ring compounds in
which the co-ordination number of phosphorus varies from
three to five have attracted considerable attention in recent
years.’-, Structural studies have been carried out on 1,3,2,4diazadiphosphetidines containing exocyclic P=O, P=S, and
P=Te bonds.2.”6 Although several 1,3,2,4diazadiphosphetidines containing exocyclic P=N bonds have been reported in
recent years,7 no X-ray crystal structure analysis has been
reported. Only the X-ray crystal structures of an anionic
cyclodiphosphazane,* [Re(CO),((RN),PZ(NR2)(NR),)I (R
Me,Si), and a cationic derivative with an exocyclic P=N bond,
[Me,Si(NR),P(NR),P(NR)(NHR)] [Re,(CO),(p-Cl),] (R = Me,Si), have been reported. We now report the synthesis
and structural analysis of a bis(imino)cyclodiphosphazane and
compare its structural features with those of [(Pri2N)2To=N]z,
the first cyclodiphosphazene isolated by Baceiredo et al.
7
Table 1. Selected structural parameters (lengths in
C(Ph”NMe,)(NPh)l,
(2)
A, angles in ”) for
P-N( 1)
P-N(2)
P-N(2’)
1.51 8(2)
1.699(2)
1.698(2)
P-N(3)
p...p/
1.625(2)
2.574(1)
N(l)-P-N(2)
N(l)-P-N(3)
N(2)-P-N(3)
N(2)-P-N(2’)
P-N(1)-C(11)
121.4(1)
107.8(1)
111.1(1)
81.5(1)
128.7(2)
P-N(2)-C(21)
P-N( 2)-P’
P-N(3)-C( 1)
P-N( 3)-C(2)
C(l)-N(3)<(2)
130.8(2)
9 8 3 1)
123.3(2)
1 21.3(3)
115.1(3)
+
Results and Discussion
Reaction of trans-[(PhN)P(NMez)12, (l),” with PhN, in
boiling toluene affords trans-[(PhN)P(NMe,)(NPh)], (2). The
Ph
(1)
i.r. spectrum of (2) exhibits a band at 1365 cm-’ which is
assigned to the exocyclic P=N vibration. The ‘H n.m.r.
spectrum shows only a single doublet at 6 2.65 (JPH= 11 Hz)
for “Me,’ protons indicating the presence of only one isomer.
The 31P-(1H) n.m.r. spectrum consists of a singlet at 6 -23.6
p.p.m. A single-crystal X-ray analysis reveals the trans configuration of the dimethylamino and consequently the phenylimino
groups (see below). Thus the Staudinger reaction of the diazadiphosphetidine (1) proceeds with net retention of configuration
at the phosphorus centres.
The structure of compound (2) is shown in the Figure and
selected bond lengths and angles are given in Table 1. The
molecule is centrosymmetric. The four-membered N2P2ring is
virtually planar. The phenyl rings attached to the ring nitrogen
atoms are coplanar with the N,P, ring (dihedral angle 1.0”).
The ring nitrogen atoms and the nitrogen atoms of the dimethylamino groups are trigonal planar, with the angles around
each nitrogen atom summing to ca. 360”. The phosphorus
atoms adopt a distorted tetrahedral geometry. Within the N2Pz
ring, the P-N distances and P-N-P and N-P-N bond angles
are close to those observed for cyclodiphosphazanes with
exocyclic P=S bonds.’
Ph
I
t 2,4-Bis(dimethylamino)-1,3-diphenyl-2,4-bis(phenylimino)1,3,2h5,4h5-diazadiphosphetidine.
1A preliminary account of this work was presented at the 5th
International Symposium on Inorganic Ring Systems, Amherst,
Massachusetts, August 1988.
Supplementary data available: see Instructions for Authors, J. Chem.
SOC.,Dalton Trans., 1990, Issue 1, pp. xix-xxii.
1120
J. CHEM. SOC. DALTON TRANS.
1990
Table 2. Atomic positional parameters for [(PhN)P(NMe,)(NPh)]2,
(2), with estimated standard deviations in parentheses
Xla
Figure. Perspective view of the molecule [(PhN)P(NMe,)(NPh>l2,(2)
0.571 08(6)
0.528 l(2)
0.553 9(2)
0.747 6(2)
0.848 6(4)
0.819 5(5)
0.387 l(3)
0.265 5(3)
0.127 6(3)
0.110 l(4)
0.231 l(5)
0.368 9(3)
0.628 8(2)
0.594 6(3)
0.668 9(3)
0.777 9(3)
0.812 5(3)
0.739 O(2)
Ylb
0.623 Ol(9)
0.748 4(3)
0.429 4(2)
0.663 2(2)
0.782 8(5)
0.569 5(8)
0.763 6(3)
0.860 5(4)
0.876 5(5)
0.800 4(5)
0.706 l(5)
0.689 5(4)
0.337 8(3)
0.180 9(3)
0.092 2(4)
0.160 2(3)
0.316 3(4)
0.406 4(3)
ZlC
0.978 79(4)
0.923 5(1)
0.958 7(1)
1.015 8(1)
0.990 l(3)
1.073 7(3)
0.878 1(1)
0.897 l(1)
0.852 6(2)
0.789 2(2)
0.769 3(2)
0.812 8(1)
0.908 6(1)
0.900 5(1)
0.851 5(1)
0.810 0(1)
0.818 2(1)
0.867 l(1)
(H atoms omitted)
It is worthwhile to compare the structural features of
compound (2) with those of (3), the first stable cyclodiphosphazene for which the X-ray structure is known." Both compounds contain phosphorus centres bonded to four nitrogen
atoms. In the case of (3) the N,P, ring is planar and the
exocyclic nitrogen atoms are trigonal planar. All endo- and
exo-cyclic P-N bond lengths are equal (1.650 A) and it is
(3) R = Pr'
suggested that unsaturation is evenly delocalised over the ring
skeleton and the exocyclic nitrogen atoms. By contrast, three
different P-N bond lengths are observed for the bis(imino)
derivative (2). The endocyclic P-N bonds are the longest
(1.700 A) presumably as a result of the competition for the lone
pair of electrons on the nitrogen by the aryl group; the exocyclic
P-NMe, bonds are shorter (1.625 A) signifying appreciable
multiple-bond character. The exocyclic P=N bonds are the
shortest (1.518 %I) and this value indicates that the exocyclic
P=N bond is not delocalised with the N2P, ring system. The
effect of multiple bonding within the N,P2 ring in (3) is also
reflected in the considerable widening of the endocyclic angle
at phosphorus (N-P-N) and a corresponding decrease in the
P-N-P angle (95.0 and 85.0" respectively) compared to the
values for compound (2) (81.5 and 98.5" respectively). Such a
trend (uiz. increase in the ring N-P-N angle and decrease in
P-N-P angle with strengthening of skeletal n: bonding) is well
documented for cyclotri- and cyclotetra-phosphazene derivatives, (NPX,), (n = 3 or 4).',
Experimental
The i.r. spectrum (4 000--400 cm-') was recorded using a CarlZeiss UR-10 spectrometer, the 'H n.m.r. spectrum on a Bruker
FT-270 (270 MHz) spectrometer with SiMe, as the internal
standard, and the 3 1P n.m.r. spectrum at 32.2 MHz on a Varian
FT-80A spectrometer, chemical shifts downfield from the
external standard, 85% H3P04, being assigned positive values.
Elemental analyses were performed at the City University,
London, by Dr. S. A. M a t h . Phenyl azide', and trans[(PhN)P(NMe,)], " were prepared by literature methods.
Synthesis of [(PhN)P(NMe,)(NPh)],
(2).-Phenyl
azide
(0.72 g, 6 mmol) was added to a solution of [(PhN)P(NMe,)],
(1) (1.0 g, 3 mmol) in toluene (15 cm3). After effervescence
(caused by evolution of N2) had ceased (ca. 10 min), the solution
was heated under reflux for 12 h and filtered. The filtrate was
cooled to obtain the required compound (0.95 g, 61%) as
colourless crystals. Recrystallisation from dichloromethane
gave well formed crystals suitable for X-ray structure determination, m.p. 186-194 "C (decomp.) (Found: C, 64.5; H, 6.3;
N, 16.2. C,,H,,N,P,
requires C, 65.4; H, 6.2; N, 16.3%). 1.r.
spectrum (Nujol mull): 1 595s, 1495s, 1365s, 1 285s, 1 275s,
1 205w, 1 195w, 1 115s, 1095m, 1080w, 1040w, 1015s, 1 OlOs,
965s, 930s, 905w, 770m, 705w, 550w, 530w, and 480s cm-'.
N.m.r.: 'H (CDCI,), 6 2.65 (d with virtual coupling, JPH= 11
Hz) and 6.70-7.50 (m); ,'P-{ 'H) (CHCI,), 6 - 23.6 (s) p.p.m.
Crystallographic Studies.-Crystal data. C,,H,,N,P,,
A4 =
514, monoclinic, space group P2,/n (alternative P2,lc, no. 14),
a = 8.405(2), b = 8.536(1), c = 18.844(3) A, p = 94.51(2)",
U = 1347.8 A3, 2 = 2, D, = 1.268 g cm-,, F(OO0) = 544,
h = 0.709 26 A, p(Mo-K,) = 1.942 cm-', crystal size =
0.4 x 0.3 x 0.3 mm.
Data collection. An Enraf-Nonius CAD-4 four-circle diffractometer with graphite-monochromatised Mo-K, radiation was
used to measure the unit-cell dimensions and to collect the data.
The unit-cell constants were obtained by least-squares analysis
of the diffractometer setting angles of 25 well centred reflections
with 20 < 28 < 28". The intensities of 3 213 reflections with
4 < 28 < 50" were recorded using -28
scans. Of these, 2 364
reflections were unique and 1424 had Z > 20 ( I ) . The
intensities were reduced to a standard scale using routine
procedures. l4 Corrections for Lorentz and polarisation factors
were applied, but not for absorption. Scattering factors for
neutral atoms were taken from ref. 15 and were corrected for
the real and imaginary parts of anomalous dispersion.
Structure solution and rejinement. The structure was solved
by direct methods (MULTAN 80)', from which phosphorus,
nitrogen, and most carbon atom positions were obtained. The
remaining non-hydrogen-atom positions were determined from
a Fourier difference synthesis. Refinement was carried out by
using the SHELX 76 system.I7 The structure was refined
initially by a full-matrix least-squares procedure with independent isotropic thermal parameters for the heavy atoms. Only the
hydrogen atoms of the phenyl rings could be seen in a Fourier
difference synthesis, and all hydrogen atoms were placed in their
J. CHEM. SOC. DALTON TRANS.
1990
geometrically correct positions (C-H 1.08 A). The hydrogen
atoms were then allowed to refine freely with satisfactory
results. The final refinements were with anisotropic thermal
parameters for the non-hydrogen atoms and isotropic
parameters for the hydrogen atoms and the positions of all
atoms free to refine. A three-block-matrix least-squares method
was employed minimising ZwAF2 where w-’ = 021FoI +
O.0O11F,J2.The refinement converged at R = 0.036, R’ = 0.035
for 1 413 unique observed reflections [ I > 2 0 ( 1 ) ] and 229 leastsquares parameters. Eleven reflections were omitted because of
suspected extinction. The final difference maps were flat,
without recognisable residual features. The final atomic
positional parameters of the non-hydrogen atoms are given in
Table 2.
Additional material available from the Cambridge Crystallographic Data Centre comprises H-atom co-ordinates, thermal
parameters, and remaining bond distances and angles.
Acknowledgements
Thanks are due to the Council of Scientific and Industrial
Research, New Delhi, India for a fellowship (to S . S . K.) and the
International Organisation of Chemical Sciences in Development (IOCD) (City University, London) for elemental analyses.
References
1 S. S. Kumaravel, S. S. Krishnamurthy, T. S. Cameron, and A. Linden,
Inorg. Chem., 1988,27,4546 and refs. therein.
2 R. A. Shaw, Phosphorus Sulfur, 1978,4,101 and refs. therein.
3 R. R. Holmes, ACSMonogr., 1980,175.
4 P. G. Owston, L. S. Shaw, R. A. Shaw, and D. A. Watkins, J. Chem.
Soc., Chem. Commun., 1982,16.
1121
5 D. E. Coons, V. S. Allured, M. D. Noirot, R. C. Haltiwanger, and
A. D. Norman, Inorg. Chem., 1982,21, 1947 and refs. therein.
6 S. Pohl, Z. Naturforsch., Teil B, 1979,34,256.
7 0. J. Scherer, P. Klausmann, and M. Kuhn, Chem. Ber., 1974, 107,
552; E. Niecke and W. Bitter, ibid., 1976,109,415; 0.J. Scherer and
G. Schnabel, ibid., p. 2996; R. Appel and J. Halstenberg, ibid., 1977,
110,2374; E. Niecke and D. A. Wildbredt, ibid., 1980,113, 1549;A. P.
Marchenko, V. A. Kovenya, and A. M. Pinchuk, Zh. Obshch. Khim.,
1980,50,226; R. H. Neilson, Inorg. Chem., 1981,20, 1679; E. Niecke,
K. Schwichtenhoevel, H. G. Schaefer, and B. Krebs, Angew. Chem.,
Int. Ed. Engl., 1981, 20, 963; E. Niecke and H. G. Schaefer, Chem.
Ber., 1982, 115, 185; X. M. Xie and R. H. Neilson, Organometallics,
1983, 2, 921; E. Niecke, R. Rueger, B. Krebs, and M. Dartmann,
Angew. Chem., Int. Ed. Engl., 1983, 22, 552; J. Boeske, E. Niecke,
E. Ocando-Mavarez, J-P. Majoral, and G. Bertrand, Znorg. Chem.,
1986,25,2695.
8 0. J. Scherer, J. Kerth, and M. L. Ziegler, Angew. Chem., Int. Ed.
En& 1983,22, 503.
9 0.J. Scherer, P. Quintus, and W. S. Sheldrick, Chem. Ber., 1987,120,
1183.
10A. Baceiredo, G. Bertrand, J-P. Majoral, G. Sicard, J. Jaud, and
J. Galy, J. Am. Chem. Soc., 1984, 106,6088.
11 G. Bulloch, R. Keat, and D. G. Thompson, J. Chem. Soc., Dalton
Trans., 1977,99.
12 S. S. Krishnamurthy, A. C. Sau, and M. Woods, Adv. Inorg. Chem.
Radiochen., 1978, 21,41.
13 ‘Organic Syntheses,’Wiley, New York, 1955, Coll. vol. 3, p. 710.
14 T. S. Cameron and R. E. Cordes, Acta Crystallogr., Sect. B, 1979,35,
749.
15 ‘International Tables for X-Ray Crystallography,’ Kynoch Press,
Birmingham, 1974, vol. 4.
16 G. Germain, P. Main, and M. M. Woolfson, Acta Crystallogr., Sect.
A, 1971,27,368.
17 G. M. Sheldrick, SHELX 76, Program for Crystal Structure
Determination, University of Cambridge, 1976.
Received 12th May 1989; Paper 9/01997T